Method for detackification of paint spray operation wastes

ABSTRACT

An improved method for detackifying over-sprayed paint, lacquer or enamel entrained in the circulating water of paint spray booths comprises maintaining in the wash water a small amount of an alkaline zinc solution containing ammonium hydroxide and ammonium chloride.

This is a division of application Ser. No. 077,524, filed July 24, 1987now U.S. Pat. No. 4,759,855.

BACKGROUND OF THE INVENTION

Automobile parts, bicycles, toys, appliances and other industrial andconsumer articles are conventionally spray painted in areas called spraybooths wherein water curtains are employed to wash the air and to removeover-sprayed paint, lacquer or enamel solids. The wash water is thentreated to remove paint solids, and the treated water is recirculated.

A water curtain is typically created by pumping water into a troughabove the overspray area. The overflow from the trough is thencontrolled so that a uniform sheet of water falls along the length ofthe trough and down the booth's wall. Spray nozzles are also commonlyused. Droplets of oversprayed paint, emitted by a spray gun, contact andare captured by the water curtain.

A major problem associated with spraying operations concerns the tackyor adhesive nature of the over-sprayed coating materials. Solids tend toagglomerate and accumulate on the walls, ceiling and floor of the sprayarea and to clog water spray equipment, recirculating pumps and thelike. Thus, the overspray, or paint mist, captured in the water systemof a spray booth must be detackified, or "killed", before it adheres tothe walls, piping, etc. of the spray booth. Paint that sticks to spraybooth surfaces usually cannot be easily removed from the equipment andtends to build up overtime, which hampers spray booth efficacy.

The term "paint killing", as used herein, refers to the act ofdetackifying oversprayed paint in paint spray booths.

"Paint", as used herein, is a generic term which encompasses all commonvarieties of water insoluble coatings commonly applied in sprayingoperations, including but not limited to oil base paints, enamels andlacquers. These products, if untreated, readily adhere to the walls ofspray booths and any other surface that they contact, such as thesurfaces of water distribution piping, spray nozzles etc.

One solution which has been found to have practical application to theproblem involves the use of chemicals which, when added to spray boothwater, detackify paint solids. A wide, variety of chemicals have beenproposed for this purpose, including compositions containing polymersand multi-valent metal salts which form insoluble hydroxides at pH'sgreater than about 7. The use of combinations of this type are describedin U.S. Patents: U.S. Pat. Nos. 3,861,887 to Forney; 3,990,986 to Gabelet al; 4,002,490 to Michalski et al; 4,130,674 to Roberts et al; and4,440,647 to Puchalski. While these compositions are generally effectivein detackifying and removing paint over-spray, a need exits forwater-based, stable alkaline compositions which have high efficiency inorder to increase productivity and to achieve a high degree ofeffectiveness for all types of paints and particularly solvent-bornepaints, lacquers and enamels.

DETAILED DESCRIPTION OF THE INVENTION

The instant invention relates to the use of stable, alkaline/zincsolutions as detackifiers of water-borne paints. The effectiveness ofthese compositions depends on the ability of zinc to precipitate as zinchydroxide upon dilution by the system being treated and alkalinity to"kill" entrained paints.

More particularly, the present invention relates to an improved methodfor detackifying over-sprayed paint entrained in the circulating waterof water wash paint spray booths. The improvement comprises adding tothe water being circulated in a paint spray booth operation an effectiveamount, for the purpose of detackifying and removing over-sprayed paint,a stable, alkaline zinc solution which comprises a zinc salt, ammoniumhydroxide, ammonium chloride and water, and which precipitates zinchydroxide when diluted by the wash water. The zinc hydroxide absorbspaint particles and then floats them to the surface of the system beingtreated, while the alkalinity detackifies the paint.

Thus, the instant invention additionally relates to paint-detackifyingcompositions comprising a zinc salt, ammonium hydroxide, ammoniumchloride and water.

Any zinc source can be used. The preferred zinc sources are salts suchas zinc chloride and zinc oxide. To formulate the instant products,which are aqueous solutions, the zinc source is added to water so as tocomprise 0.1 to 25% of the total composition weight, preferably 0.5-10%.Ammonium chloride and ammonium hydroxide are then added. The ammoniumchloride should comprise 1-10% of the total composition weight and theammonium hydroxide should comprise 1-20% of the total compositionweight, preferably 1-5% and 1-10%, respectively. Order of addition ofthe zinc salt, ammonium chloride and ammonium hydroxide is not critical.

The ammonium ions solubilize the zinc in the concentrated alkalinesolutions of the instant invention.

Additionally the ammonium chloride and ammonium hydroxide raise the pHof the zinc solution from about 7 to about 8.5 to 10.5, preferably9.0-10.0. Even though the composition is strongly alkaline, the zincremains in solution. The compositions are thus applied at a high pH, ina stabilized form.

Use of the instant solutions as detackifiers for paint spray operationwaters is typically carried out by adding the stable, high pH aqueouszinc solution to fresh or recirculated water at a convenient location inthe system being treated, such as at a sump, upstream from the pumps orat any advantageous location in the recirculation system, but preferablybefore the water enters the spray area circuit of the system beingtreated. Addition of the instant compositions to the system beingtreated dilutes the ammonium ion concentration, and precipitation ofzinc hydroxide immediately occurs. The zinc hydroxide absorbs paintparticles and floats them to the surface, while the alkalinitydetackifies the paint. This facilitates easy removal of the paint/zinchydroxide complex and recirculation of the wash water.

An effective amount of the instant composition should be added to thespray booth water system. As used herein, the term "effective amount" isthat amount which is sufficient to absorb all captured paint and todetackify the paint solids so that they can be readily separated fromthe wash water. Since the amount of paint contacting a water curtainvaries depending on a number of variables, including plant or processshutdowns, the size of the items being painted, spraying techniques,waterflow rate and the type of paint being used, the amount of paintthat is captured can vary considerably. Under normal conditions thedosage level is within the range of 0.1 to 5 oz/gal of water circulated,preferably 0.5 to 2.0 oz/gal of water circulated.

As indicated above, this invention does not require the presence ofpolymers or other additives to achieve high performance and efficiency.Such additives, however, have not been found to detract from theadvantages realized by this invention and may under exceptionalconditions provide marginal improvement with certain custom sprayformulations. Typical water-soluble polymers of this type include thewater-soluble cationic polymers such as quaternary ammonium polymers,which tend to coagulate small paint particles. A preferred polymer is adimethyl diallyl ammonium chloride polymer. Other preferred additivesinclude carbonates and phosphates, which add alkalinity to the systembeing treated and N-methylpyrrolidone, which assists in coupling thepaint solids to the zinc floc.

Other additives which can be present in amounts up to about 5%, byweight, include clays, particularly bentonite, carbon black, talc, gums,starch, dextrin, lime, aluminum oxide, silica solids, casein and thelike.

EXAMPLES

The following examples demonstrate the instant invention in greaterdetail. They are not intended, however, to limit the scope of thisinvention in any way.

The following products were formulated and used in the paint-killexamples:

    ______________________________________                                                    Active Weight % in Formula                                        Ingredient    A      B      C    D    E    F                                  ______________________________________                                        Zeolite Softened Water                                                                      65.0   56.7   56.5 57.8 59.85                                                                              58.6                               Zinc Chloride 5.0    4.5    2.3  4.5  --   --                                 Zinc Oxide    --     --     --   22.5 2.7  3.0                                M--Pryol      15.0   13.6   13.6 6.5  13.6 13.6                               Ammonium Chloride                                                                           5.0    4.6    4.6  1.9  4.6  4.6                                Ammonium      10.0   10.0   12.0 --   10.0 10.0                               Hydroxide (28%)                                                               Polydimethyl diallyl                                                                        --     4.6    4.0  1.5  4.5  3.5                                ammonium chloride*                                                            Sodium Carbonate                                                                            --     6.0    7.0  0.25 4.75 4.7                                Potassium     --     --     --   0.9  --   1.0                                Tripolyphosphate                                                              Copper Nitrate                                                                              --     --     --   1.5  --   1.0                                ______________________________________                                         *MW = approximately 500,000, available from Calgon Corporation as CatFloc     C.                                                                       

The above formulations were prepared by mixing the appropriate amountsof ingredients in the order given. These formulations were then added tobeakers containing 200 ml of water at a dosage of 1.0 oz/gallon ofwater. 1 ml of a green, high solids commercially available enamel paintwas then added to each beaker, and the contents were mixed. Killperformance was then measured subjectively by feel.

Results of these tests are shown in Table I.

                  TABLE 1                                                         ______________________________________                                        EXAMPLE                                                                       NUMBER     FORMULA      KILL PERFORMANCE                                      ______________________________________                                        1          A            Good (slight tackiness,                                                       no paint remained on                                                          hand)                                                 2          B            Good (slight tackiness,                                                       no paint remained on                                                          hand)                                                 3          C            Fair (slight tackiness,                                                       some paint remained on                                                        hand, but was easily                                                          removed by wiping)                                    4          D            Good (slight tackiness)                                                       no paint remained on                                                          hand)                                                 5          E            Excellent (no tacki-                                                          ness)                                                 6          F            Excellent (no tacki-                                                          ness)                                                 ______________________________________                                    

What is claimed is:
 1. A paint detackifying composition which consistsessentially of: 0.1 to 25%, by weight, a zinc salt, 1 to 20%, by weight,ammonium hydroxide, 1 to 10%, by weight, ammonium chloride, and thebalance water.